It is known to control an infinitely variable V-belt transmission with a fluid control valve assembly which supplies fluid to and relieves fluid from a cylinder space the volume of which controls the transmission ratio by adjusting the axial position of a first conical sheave portion relative to a second conical sheave portion. The control valve assembly includes a valve housing and an internal, displaceable valve body. Such control apparatus is known from U.S. Pat. No. 4,152,947 where, depending on a spring load and a fluid pressure, a fluid flow is conducted to the operating cylinder of the variable V-belt transmission, because the valve body upon axial displacement closes or opens passages. In this known design the spring load is regulated by mechanical means and by a fluid pressure which is governed by the input speed of the V-belt transmission.
The operation of the control valve by means of mechanical signals limits the adjustability of the control valve, because such mechanical signals generally allow of only limited variation.